CPP read sensor having constrained current paths made of lithographically-defined conductive vias with surrounding oxidized metal sublayers

ABSTRACT

Current-perpendicular-to-plane (CPP) read sensors having constrained current paths made of lithographically-defined conductive vias with surrounding oxidized metal sublayers, and methods of making the same, are disclosed. In one illustrative example, at least part of a sensor stack structure which includes an electrically conductive spacer layer is formed. A metal (e.g. Ta) sublayer is then deposited over and adjacent the spacer layer, followed by one of an oxidation process, a nitridation process, and an oxynitridation process, to produce an insulator (e.g. TaOx) from the metal sublayer. The metal sublayer deposition and oxidation/nitridation/oxynitridation processes are repeated as necessary to form the insulator with a suitable thickness. Next, a resist structure which exposes one or more portions of the insulator is formed over the insulator. With the resist structure in place, exposed insulator materials are removed by etching to form one or more apertures through the insulator down to the spacer layer. Electrically conductive materials are subsequently deposited within the one or more apertures to form one or more lithographically-defined conductive vias of a current-constraining structure. Advantageously, the lithographically-defined conductive vias increase the current density of the read sensor in the region of the sensing layers to thereby simultaneously increase its resistance and magnetoresistance. With use of the process of oxidation, nitridation, or oxynitridation on each metal sublayer, degradation of the spacer layer is reduced or eliminated such that the desirable soft magnetics of the sensing layers in the read sensor are maintained.

BACKGROUND

1. Field of the Technology

The present disclosure relates generally to read sensors of magneticheads in data storage devices, and more particularly to read sensors ofthe current-perpendicular-to-plane (CPP) type having constrained currentpaths made of lithographically-defined conductive vias with surroundingoxidized metal layers.

2. Description of the Related Art

Today's computer devices often include auxiliary memory storage deviceshaving media on which data can be written and from which data can beread for later use. A direct access storage device (disk drive)incorporating rotating magnetic disks are commonly used for storing datain magnetic form on the disk surfaces. Data is recorded on concentric,radially spaced tracks on the disk surfaces. Magnetic heads whichinclude read sensors are then used to read data from the tracks on thedisk surfaces.

Magnetoresistive (MR) read sensors, commonly referred to as MR heads,are used in high capacity disk drives and may read data from a surfaceof a disk at greater linear densities than thin film inductive heads. AnMR sensor detects a magnetic field through the change in the resistanceof its MR sensing layer (also referred to as an “MR element”) as afunction of the strength and direction of the magnetic flux being sensedby the MR layer. Recorded data can be read from a magnetic mediumbecause the external magnetic field from the recorded magnetic medium(the signal field) causes a change in the direction of magnetization inthe MR element, which in turn causes a change in resistance in the MRelement and a corresponding change in the sensed current or voltage.Within the general category of MR sensors is the giant magnetoresistance(GMR) sensor manifesting the GMR effect. In GMR sensors, the resistanceof the MR sensing layer varies as a function of the spin-dependenttransmission of the conduction electrons between magnetic layersseparated by a non-magnetic layer (spacer) and the accompanyingspin-dependent scattering which takes place at the interface of themagnetic and non-magnetic layers and within the magnetic layers. GMRsensors using only two layers of ferromagnetic material (e.g.nickel-iron, cobalt-iron, or nickel-iron-cobalt) separated by a layer ofnonmagnetic material (e.g. copper) are generally referred to as spinvalve (SV) sensors manifesting the SV effect.

One of the ferromagnetic (FM) layers referred to as the pinned layer hasits magnetization typically pinned by exchange coupling with anantiferromagnetic (AFM) layer (e.g., nickel-oxide, iron-manganese, orplatinum-manganese). The pinning field generated by the AFM pinninglayer should be greater than demagnetizing fields to ensure that themagnetization direction of the pinned layer remains fixed duringapplication of external fields (e.g. fields from bits recorded on thedisk). The magnetization of the other FM layer referred to as the freelayer, however, is not fixed and is free to rotate in response to thefield from the information recorded on the magnetic medium (the signalfield). The pinned layer may be part of an antiparallel (AP) pinnedstructure which includes an antiparallel coupling (APC) layer formedbetween first and second AP pinned layers. The first AP pinned layer,for example, may be the layer that is exchange coupled to and pinned bythe AFM pinning layer. By strong antiparallel coupling between the firstand second AP pinned layers, the magnetic moment of the second AP pinnedlayer is made antiparallel to the magnetic moment of the first AP pinnedlayer.

Sensors are classified as a bottom sensor or a top sensor depending uponwhether the pinned layer is located near the bottom of the sensor closeto the first read gap layer or near the top of the sensor close to thesecond read gap layer. Sensors are further classified as simple pinnedor AP pinned depending upon whether the pinned structure is one or moreFM layers with a unidirectional magnetic moment or a pair of AP pinnedlayers separated by the APC layer with magnetic moments of the AP pinnedlayers being antiparallel. Sensors are still further classified assingle or dual wherein a single sensor employs only one pinned layer anda dual sensor employs two pinned layers with the free layer structurelocated there between.

A read sensor may also be of a current-perpendicular-to-plane (CPP) typein which current flows perpendicular to the major planes of the sensorlayers. First and second shield layers engage the bottom and the top,respectively, of the sensor so as to simultaneously serve aselectrically conductive leads for the sensor. The CPP sensor may becontrasted with a current-in-plane (CIP) type sensor in which thecurrent is conducted in planes parallel to the major thin film planes ofthe sensor. In a CPP sensor, when the spacer layer between the freelayer and the AP pinned structure is nonmagnetic and electricallyconductive (such as copper), the current is referred to as a “sensecurrent”; however when the spacer layer is nonmagnetic and electricallynonconductive (such as aluminum oxide), the current is referred to as a“tunneling current”. Hereinafter, the current is referred to as aperpendicular current I_(p) which can be either a sense current or atunneling current.

All conventional metallic CPP read sensors have several shortcomings.First, their resistance-area (RA) products are quite low. For typicalsensor areas, this results in read sensors having low resistance valueswhich are poorly matched to amplifiers of the read circuitry. Inaddition, parasitic resistances from layers of the read sensor that donot contribute to the magnetoresistance (e.g. the AFM layers) lower thesignal-to-noise ratio (SNR) of the sensor. Finally, unlike magnetictunneling junction (MTJ) CPP sensors using the current I_(p) as atunneling current, the relatively low resistance of all metallic CPPsensors requires them to operate at very high current densities.However, effects such as the spin torque phenomenon and the Oerstedfield from the perpendicular current I_(p) limit current densitiessuitable for stable sensor operation.

Current densities of CPP read sensors may be increased by restrictingthe flow of the perpendicular current I_(p) through the sensor stack.Conventionally, this may be achieved by utilizing “current-screen”layers which are created by placing one or more ultra-thin insulatinglayers (a nano-oxide layer or NOL) within the sensor. Many tinyrandomly-distributed conductive pores or holes, which restrict thecurrent flow and concentrate the current density near the active layersof the sensor, are created through this process. In practice, however,the process is difficult to control and does not achieve adequate andmanufacturable results. As sensors become smaller, the sensor coverssuch a small region of the film that statistical variations in thedistribution of conductive pores, and therefore in the current densitymay cause uncontrollable and unacceptable variations in the sensorresistance.

Accordingly, there is an existing need to overcome these and otherdeficiencies of the prior art.

SUMMARY

Current-perpendicular-to-plane (CPP) read sensors having constrainedcurrent paths made of lithographically-defined conductive vias withsurrounding oxidized metal sublayers, and methods of making the same,are disclosed. In one illustrative example, at least part of a sensorstack structure which includes an electrically conductive spacer layeris formed. A metal sublayer is then deposited over and adjacent thespacer layer, followed by one of an oxidation process, a nitridationprocess, and an oxynitridation process, to produce an insulator (e.g. anoxidized metal) from the metal sublayer. The metal sublayer depositionand oxidation/nitridation/oxynitridation processes are repeated asnecessary to form the insulator with a suitable thickness. Next, aresist structure which exposes one or more portions of the insulator isformed over the insulator. With the resist structure in place, exposedinsulator materials are removed by etching to form one or more aperturesthrough the insulator down to the spacer layer. Electrically conductivematerials are subsequently deposited within the one or more apertures toform one or more lithographically-defined conductive vias of acurrent-constraining structure.

Advantageously, the lithographically-defined conductive vias increasethe current density of the read sensor in the region of the sensinglayers to thereby simultaneously increase its resistance andmagnetoresistance. With use of the process of oxidation, nitridation, oroxynitridation on each metal sublayer, degradation of the spacer layeris reduced or eliminated such that the desirable soft magnetics of thefree layer in the read sensor are maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings:

FIG. 1 is a plan view of an exemplary prior art magnetic disk drive;

FIG. 2 is an end view of a slider with a magnetic head of the disk driveas seen in plane 2-2 of FIG. 1;

FIG. 3 is an elevation view of the magnetic disk drive wherein multipledisks and magnetic heads are employed;

FIG. 4 is an isometric illustration of an exemplary prior art suspensionsystem for supporting the slider and magnetic head;

FIG. 5 is an ABS view of the magnetic head taken along plane 5-5 of FIG.2;

FIG. 6 is a partial view of the slider and a merged magnetic head asseen in plane 6-6 of FIG. 2;

FIG. 7 is a partial ABS view of the slider taken along plane 7-7 of FIG.6 to show the read and write elements of the magnetic head;

FIG. 8 is a view taken along plane 8-8 of FIG. 6 with all material abovethe coil layer and leads removed;

FIG. 9 is an enlarged isometric ABS illustration of a magnetic headhaving a current-perpendicular-to-plane (CPP) type sensor;

FIG. 10 is a flowchart which describes a fabrication process for a CPPsensor having constrained current paths made of lithographically-definedconductive vias;

FIG. 11 is the first in a series of ABS illustrations of FIGS. 11-15 ofpartially fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, showing that a read sensor stackstructure which includes an electrically conductive spacer layer isformed over a first shield layer;

FIG. 12 is the second in a series of ABS illustrations of FIGS. 11-15 ofpartially fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, which is the same as that shownin FIG. 11 except that an oxidized metal sublayer structure is formedover the spacer layer;

FIG. 13 is the third in a series of ABS illustrations of FIGS. 11-15 ofpartially fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, which is the same as that shownin FIG. 12 except a resist structure is applied and patterned on top ofthe oxidized metal sublayer structure exposing materials of thestructure;

FIG. 14 is the fourth in a series of ABS illustrations of FIGS. 11-15 ofpartially fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, which is the same as that shownin FIG. 13 except that the exposed oxidized metal materials are removedand a via is formed through the oxidized metal sublayer structure;

FIG. 15 is the fifth in a series of ABS illustrations of FIGS. 11-15 ofpartially fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, which is the same as that shownin FIG. 14 except electrically conductive materials are formed withinthe via and over the oxidized metal sublayer structure to thereby form acurrent-constraining structure having a lithographically-definedconductive via;

FIG. 16 is an ABS illustration showing a CPP read sensor of an exemplaryembodiment;

FIG. 17 is an ABS illustration showing a CPP read sensor of analternative embodiment, which is the same as that shown in FIG. 16except the current-constraining structure has twolithographically-defined conductive vias;

FIG. 18 is an ABS illustration showing a CPP read sensor of analternative embodiment, which is the same as that shown in FIG. 16except the current-constraining structure has threelithographically-defined conductive vias;

FIG. 19 is an isometric view of the CPP read sensor of the exemplaryembodiment of FIG. 16, revealing exemplary trackwidth and stripe heightdimensions of the lithographically-defined conductive via;

FIG. 20 is a top down view of the current-constraining structure of FIG.16 and 19, revealing exemplary trackwidth and stripe height dimensionsof the lithographically-defined conductive via;

FIG. 21 is a top down view of one variation on the stripe heightdimension of the lithographically-defined conductive via of FIGS. 16 and19-20;

FIG. 22 is an ABS illustration showing a CPP read sensor of analternative embodiment;

FIG. 23 is the first in a series of ABS illustrations of FIGS. 23-27 ofpartially fabricated oxidized metal sublayer structures corresponding tostep 1006 of FIGS. 10-11, showing that an electrically conductive spacerlayer is formed;

FIG. 24 is the second in a series of ABS illustrations of FIGS. 23-27 ofpartially fabricated oxidized metal sublayer structures corresponding tostep 1006 of FIGS. 10-11, which is the same as that shown in FIG. 23except that a metal sublayer is deposited over the spacer layer;

FIG. 25 is the third in a series of ABS illustrations of FIGS. 23-27 ofpartially fabricated oxidized metal sublayer structures corresponding tostep 1006 of FIGS. 10-11, which is the same as that shown in FIG. 24except that the metal sublayer is oxidized;

FIG. 26 is the fourth in a series of ABS illustrations of FIGS. 23-27 ofpartially fabricated oxidized metal sublayer structures corresponding tostep 1006 of FIGS. 10-11, which is the same as that shown in FIG. 25except that another metal sublayer is deposited over thepreviously-oxidized metal sublayer;

FIG. 27 is the fifth in a series of ABS illustrations of FIGS. 23-27 ofpartially fabricated oxidized metal sublayer structures corresponding tostep 1006 of FIGS. 10-11, which is the same as that shown in FIG. 26except that the other metal sublayer is oxidized;

FIG. 28 is a graph showing illustrative data for low field (LF) giantmagnetoresistance (GMR) versus oxygen flow pressure when tantalum (1 nmthickness) is utilized in the insulator;

FIG. 29 is a graph showing illustrative data for coercivity H_(c) (easyand hard) versus oxygen flow pressure when tantalum (1 nm thickness) isutilized in the insulator;

FIG. 30 is a graph showing illustrative data for LF GMR versus tantalumsublayer thickness;

FIG. 31 is a graph showing illustrative data for coercivity H_(ce)(easy) versus tantalum sublayer thickness; and

FIG. 32 is a graph showing illustrative data for coercivity H_(ch)(hard) versus tantalum sublayer thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Current-perpendicular-to-plane (CPP) read sensors having constrainedcurrent paths made of lithographically-defined conductive vias withsurrounding oxidized metal sublayers, and methods of making the same,are disclosed. In one illustrative example, at least part of a sensorstack structure which includes an electrically conductive spacer layeris formed. A metal sublayer is deposited over and adjacent the spacerlayer, followed by one of an oxidation process, a nitridation process,and an oxynitridation process, to produce an insulator (e.g. an oxidizedmetal) from the metal sublayer. The metal sublayer deposition andoxidation/nitridation/oxynitridation processes are repeated as necessaryto form the insulator with a suitable thickness. Next, a resiststructure which exposes one or more portions of the insulator is formedover the insulator. With the resist structure in place, exposedinsulator materials are removed by etching to form one or more aperturesthrough the insulator down to the spacer layer. Electrically conductivematerials are subsequently deposited within the one or more apertures toform one or more lithographically-defined conductive vias of acurrent-constraining structure. Advantageously, thelithographically-defined conductive vias increase the current density ofthe read sensor in the region of the sensing layers to therebysimultaneously increase its resistance and magnetoresistance. The sizeand number of vias may be varied and selected so as to precisely “tune”the sensor's resistance and magnetoresistance. As there is increasingevidence that the magnetoresistive effect is reduced near edges of theread sensor from milling damage, it is also advantageous to isolate asingle or few vias in the center of the sensor structure to avoid suchdamage. With use of the process of oxidation, nitridation, oroxynitridation on each metal sublayer, degradation of the spacer layeris reduced or eliminated such that the desirable soft magnetics of thefree layer in the read sensor are maintained.

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

General Disk Drive and Magnetic Head Architecture. Referring now to thedrawings wherein like reference numerals designate like or similar partsthroughout the several views, FIGS. 1-3 illustrate a magnetic disk drive30. Disk drive 30 includes a spindle 32 that supports and rotates amagnetic disk 34. Spindle 32 is rotated by a spindle motor 36 that iscontrolled by a motor controller 38. A slider 42 includes a combinedread and write magnetic head 40 and is supported by a suspension 44 andactuator arm 46 that is rotatably positioned by an actuator 47. Magnetichead 40 may utilize the read sensor which is made in accordance with thepresent invention. A plurality of disks, sliders, and suspensions may beemployed in a large capacity direct access storage device (DASD) asshown in FIG. 3. Suspension 44 and actuator arm 46 are moved by actuator47 to position slider 42 so that magnetic head 40 is in a transducingrelationship with a surface of magnetic disk 34. When disk 34 is rotatedby spindle motor 36, slider 42 is supported on a thin (typically, 0.05μm) cushion of air (air bearing) between the surface of disk 34 and anair bearing surface (ABS) 48. Magnetic head 40 may then be employed forwriting information to multiple circular tracks on the surface of disk34, as well as for reading information therefrom. Processing circuitry50 exchanges signals, representing such information, with head 40,provides spindle motor drive signals for rotating magnetic disk 34, andprovides control signals to actuator 47 for moving slider 42 to varioustracks. In FIG. 4, slider 42 is shown mounted to a suspension 44. Thecomponents described hereinabove may be mounted on a frame 54 of ahousing 55, as shown in FIG. 3. FIG. 5 is an ABS view of slider 42 andmagnetic head 40. Slider 42 has a center rail 56 that supports magnetichead 40, and side rails 58 and 60. Rails 56, 58 and 60 extend from across rail 62. With respect to rotation of magnetic disk 34, cross rail62 is at a leading edge 64 of slider 42 and magnetic head 40 is at atrailing edge 66 of slider 42.

FIG. 6 is a side cross-sectional elevation view of a merged magnetichead 40, which includes a write head portion 70 and a read head portion72. Read head portion 72 includes a CPP giant magnetoresistive (GMR)read head which utilizes a CPP sensor 74. FIG. 7 is an ABS view of FIG.6. CPP sensor 74 is sandwiched between ferromagnetic first and secondshield layers 80 and 82. In response to external magnetic fields, theresistance of CPP sensor 74 changes. A sense current I_(s) conductedthrough the sensor causes these resistance changes to be manifested aspotential changes. These potential changes are then processed asreadback signals by processing circuitry 50 shown in FIG. 3.

Write head portion 70 of magnetic head 40 includes a coil layer 84sandwiched between first and second insulation layers 86 and 88. A thirdinsulation layer 90 may be employed for planarizing the head toeliminate ripples in the second insulation layer caused by coil layer84. The first, second and third insulation layers are referred to in theart as an “insulation stack”. Coil layer 84 and first, second and thirdinsulation layers 86, 88 and 90 are sandwiched between first and secondpole piece layers 92 and 94. First and second pole piece layers 92 and94 are magnetically coupled at a back gap 96 and have first and secondpole tips 98 and 100 which are separated by a write gap layer 102 at theABS. Since second shield layer 82 and first pole piece layer 92 are acommon layer, this head is known as a merged head. In a piggyback headan insulation layer is located between a second shield layer and a firstpole piece layer. As shown in FIGS. 2 and 4, first and second solderconnections 104 and 106 connect leads from spin valve sensor 74 to leads112 and 114 on suspension 44, and third and fourth solder connections116 and 118 connect leads 120 and 122 from the coil 84 (see FIG. 8) toleads 124 and 126 on suspension 44.

FIG. 9 is an enlarged ABS illustration of the prior art read headportion shown in FIG. 7. The read head includes the CPP sensor 74. Firstand second insulation layers 127 and 128, such as alumina, cover thefirst shield layer 80 on each side of the sensor 74 as well as slightlycovering first and second sidewalls 130 and 132 of the sensor. First andsecond hard bias layers (HB) 134 and 136 are on the insulation layers127 and 128 and are adjacent the side walls 130 and 132. Metallic seedlayers (not shown in FIG. 9) are formed between insulator layers 127 and128 and hard bias layers 134 and 136. The hard bias layers 134 and 136cause magnetic fields to extend longitudinally through the sensor 74 forstabilizing the free layer. The sensor 74 and the first and second hardbias layers 134 and 136 are located between ferromagnetic first andsecond shield layers 80 and 82 which may serve as leads for conductingthe perpendicular current I_(p) through the sensor 74.

General Process for Current-Constraining Structure Formation of FIGS.10-16. FIG. 10 is a flowchart which describes a fabrication process foran exemplary CPP read sensor having a current-constraining structuremade of one or more lithographically-defined conductive vias. FIGS.11-16, which are a series of ABS illustrations showingpartially-fabricated sensor structures corresponding to the stepsdescribed in the flowchart of FIG. 10, will be referred to incombination with the flowchart steps of FIG. 10.

Beginning at a start block 1002 of FIG. 10 in combination with FIG. 11,at least a portion of a CPP sensor stack structure 1100 having anelectrically conductive spacer layer portion (SP-1) 1132 is formed overa first shield layer (S1) 1172 (step 1004 of FIG. 10). CPP sensor stackstructure 1100 may be made of any suitable sensor materials and, in thisembodiment, includes (from bottom to top) a seed layer (SL) 1112, anantiferromagnetic (AFM) pinning layer 1114, a pinned layer structure1104, and spacer layer portion (SP-1) 1132. In this “bottom-SV”exemplary configuration, pinned layer structure 1104 is formed beneathand adjacent spacer layer portion 1132 and over and adjacent AFM pinninglayer 1114. AFM pinning layer 1114 is formed beneath and adjacent pinnedlayer structure 1104 and over and adjacent to seed layer 1112. Seedlayer 1112 is formed over and adjacent first shield layer 1172 andunderneath AFM pinning layer 1114 for promoting an improved texture ofthe layers deposited thereon. In this embodiment, spacer layer portion1132 will form only a bottom portion or bottom sublayer (SP-1) of theentire spacer layer structure of the resulting CPP read sensor. Spacerlayer portion 1132 is highly-conductive and non-magnetic, and may bemade of suitable materials such as copper (Cu) or gold (Au).

A special iterative process 1190 is then utilized to form an insulatormade of an oxidized metal sublayer structure over and adjacent spacerlayer portion 1132 (step 1006 of FIG. 10). This process 1190 will bedescribed in more detail later in relation to FIGS. 23-27. The result isshown in FIG. 12, where an insulator 1140 made of the oxidized metalsublayer structure is formed in contact with spacer layer portion 1132.The oxidized metal sublayer structure of insulator 1140 includes aplurality of thin oxidized metal sublayers, each sublayer of which makesdirect contact with its adjacent sublayer. Since it will form part ofthe spacer layer structure, insulator 1140 is formed with a very smallthickness such as between 10 Angstroms (Å) and 100 Å. Insulator 1140 maybe formed with any suitable oxidized metal sublayers, such as oxidizedtantalum (TaOx) sublayers. Other metal sublayers, described later below,may be suitable as well. As will be described later in furthervariations, insulator 1140 may alternatively be made of a plurality ofnitrided metal sublayers, or a plurality of oxynitrided metal sublayers.

A resist structure formation process 1290 is then performed, where inFIG. 13 a resist structure 1392 is applied and patterned over andadjacent insulator 1140 exposing insulator materials 1142 of insulator1140 (step 1008 of FIG. 10). Resist structure 1392 may be made from aphotoresist. Alternatively, resist structure 1392 may be made from aresist which is compatible with electron beam (e-beam) lithographyprocesses. Although resist structure 1392 is shown and described as amonolayer resist, it may alternatively be a multi-layered resist (e.g.bilayer or trilayer resist). As shown, resist structure 1392 is formedto define an opening having an appropriate width W₁₃ for asubsequently-formed lithographically-defined conductive via. Ifphotolithography is used to form resist structure 1392, a thin film ofresist is light-exposed in regions which are to be removed, provided theresist is a positive resist. If the resist is a negative resist, it islight-exposed in regions that are to be retained. Finally, the resist issubjected to a basic developer solution. If electron beam (e-beam)lithography is used to form resist structure 1392, a thin film of resistis e-beam-exposed in regions which are to be removed, provided theresist is a positive resist. If the resist is a negative resist, it islight-exposed in regions that are to be retained. Finally, the resist issubjected to a suitable developer solution. Width W₁₃, which willultimately determine the width of the resulting conductive via, may bewithin 3 and 40 nanometers (nm). In this embodiment, only a singleopening is formed within a center of resist structure 1392 (which is ata centerline of the width of sensor stack structure 1100 and thetrackwidth of the resulting read sensor). However, the number ofopenings will vary depending on the number of vias desired.

With resist structure 1392 in place, an etching process 1390 (e.g. ionmilling) is utilized to remove exposed insulator materials 1142 throughthe opening of resist structure 1392 (step 1010 of FIG. 10). The resultis shown in FIG. 14, where an aperture 1482 is formed down to the top ofspacer layer portion 1132 to expose electrically conductive materials1432 thereof. If the etching is performed along the entire stripe height(SH) dimension, the insulator layer may be completely separated intofirst and second insulator layer portions 1442 and 1444. The ion millingprocess is discontinued once the top of spacer layer portion 1132 isreached, where electrically conductive materials 1432 of spacer layerportion 1132 are exposed. Thus, aperture 1482 is formed down through theentire insulator layer, is surrounded by insulator layer portions 1442and 1444, and has substantially the same width W₁₃ as the opening of theresist structure. FIG. 14 also reveals that the resist structure may beremoved at this time using a suitable solvent or other suitabletechnique.

A deposition process 1490 is then performed to deposit electricallyconductive materials within aperture 1482 over exposed electricallyconductive materials 1432 (step 1012 of FIG. 10). The result is shown inFIG. 15, where electrically conductive materials 1534 are not onlyformed within aperture 1482 but also over insulator layer portions 1442and 1444. As a result, a lithographically-defined conductive via 1582 ofa current-constraining structure 1580 is formed. Electrically conductivematerials 1534 which are formed above lithographically-definedconductive via 1582 and over insulator portions 1442 and 1444 form a topportion or top sublayer (SP-2) of the entire spacer layer structure. Inthis embodiment, only a single via is formed within a center of thestructure (which is at a centerline of the width of sensor stackstructure 1100 and the trackwidth of the resulting read sensor).However, the number of vias will vary depending on the design. Note thatdeposition process 1490 of FIG. 14 may alternatively be performed withresist structure 1392 kept in place until aperture 1432 is filled withthe electrically conductive materials to form a flat top surface withinsulator portions 1442 and 1444. After aperture is filled with theelectrically conductive materials to form the via, resist structure 1392is removed and the remaining electrically conductive materials aredeposited to form the top sublayer of the spacer layer.

The method corresponding to the steps described in the flowchart of FIG.10 ends at an end block 1014, but additional processing steps may besubsequently performed. For example, additional manufacturing processes1590 are utilized to complete the formation of the CPP read sensor,shown in FIG. 16 as a CPP read sensor 1600. These processes 1590 mayutilize any suitable techniques known in the art (conventional orotherwise) to complete the manufacturing per the design requirements.

As shown in FIG. 16, the resulting CPP read sensor 1600 made from theabove-described methods has a sensor stack structure 1602 (“bottom-SV”)formed in a central region 1652 surrounded by end regions 1650 and 1654.Sensor stack structure 1602 includes, from bottom to top, a seed layer1612, an AFM pinning layer 1614, a pinned layer structure 1604, acurrent constraining structure 1680, a sensing layer structure (F) 1624and a capping layer 1620. Capping layer 1620 is formed below andadjacent second shield layer 1674 and over and adjacent sensing layerstructure 1624. Sensing layer structure 1624 is formed below andadjacent capping layer 1620 and over and adjacent current-constrainingstructure 1680. Current-constraining structure 1680 is formed below andadjacent sensing layer structure 1624 and above and adjacent pinnedlayer structure 1604. Pinned layer structure 1604 is formed below andadjacent current-constraining structure 1680 and over and adjacent AFMpinning layer 1614. AFM pinning layer 1614 is formed below and adjacentpinned layer structure 1604 and over and adjacent seed layer 1620. Seedlayer 1612 is formed over and adjacent first shield layer 1172 and belowand adjacent AFM pinning layer 1614 for promoting an improved texture ofthe layers deposited thereon. CPP read sensor 1600 has first and secondinsulator layers 1660 and 1662 formed in end regions 1650 and 1654 overand adjacent first shield layer 1172, as well as, sidewalls of sensorstack structure 1602. Furthermore, CPP read sensor 1600 has first andsecond hard bias layers 1664 and 1666 formed over and adjacent insulatorlayers 1660 and 1662. Finally, second shield layer (S2) 1674 is shownformed over the planarized structure.

Note that, instead of current-constraining structure 1680 being formedwithin the entire spacer layer, it may be formed on top of or below thespacer layer. In this variation, the lithographically-defined conductivevia may be formed from the same or different non-magnetic conductivematerials of the spacer layer or from the ferromagnetic materials of theunderlying/overlying magnetic layers.

A CPP read sensor having current-constraining structure with one or morelithographically-defined conductive vias has advantages. Mostimportantly, the lithographically-defined conductive vias increase thecurrent density of the read sensor in the region of the sensing layersto thereby simultaneously increase its resistance and magnetoresistance.Especially as the dimensions of read sensors are decreasing, a tightercontrol over the current density requirement of the read sensor may beachieved by design and during fabrication. The size and number of viasmay be varied and selected so as to precisely “tune” the sensor'sresistance and magnetoresistance. As there is increasing evidence thatthe magnetoresistive effect is reduced near edges of the read sensorfrom milling damage, it is also advantageous to isolate a single or fewvias in the center of the sensor structure to avoid such damage.

Materials, Structure, and Variations on the Conductive Vias in FIGS.16-21. The following materials may be utilized in CPP read sensor 1600of FIG. 16. First and second shields 1172 and 1674 may be made of anysuitable material such as nickel-iron (NiFe); seed layer 1612 may haveone or more layers of any suitable material such as nickel-iron-chromium(NiFeCr) or NiFe; AFM pinning layer structure 1614 may be made of anysuitable material, such as platinum manganese (PtMn) or alternativelyiridium manganese (IrMn); pinned layer structure 1604 may be made of anysuitable material such as cobalt (Co) or cobalt-iron (CoFe) or Heusleralloys (e.g. Co₂MnGe); electrically conductive portions 1632 and 1634 ofcurrent-constraining structure 1680 may be made of any suitable materialsuch as copper (Cu) or gold (Au), while insulating portions 1642 and1644 of current-constraining structure 1680 may be made of any suitablematerial such as oxidized tantalum (TaOx); sensing layer structure 1624may be made of any suitable material such as CoFe or alternatively NiFeor Heusler alloys (e.g. Co₂MnGe); capping layer 1620 may be made of anysuitable material such as tantalum (Ta); first and second insulatorlayers 1660 and 1662 may be made of any suitable material such as Al₂O₃;first and second hard bias layers 1664 and 1666 may be made of anysuitable material such as cobalt-platinum-chromium (Co—Pt—Cr) or otherCo-based alloy.

The following thicknesses of the various layers may be utilized in CPPread sensor 1600. First and second shields 1172 and 1674 may have athickness range of about 30 nm to about 500 nm; seed layer 1612 may havea thickness range of about 10 Å to about 100 Å; AFM pinning layerstructure 1614 may have a thickness range of about 30 Å to about 300 Å;pinned layer structure 1604 may have a thickness range of about 10 Å toabout 100 Å; electrically conductive portions 1632 and 1634 ofcurrent-constraining structure 1680 may have a thickness range of about2 Å to about 10 Å respectively, insulating portions 1642 and 1644 ofcurrent-constraining structure 1680 may have a thickness range of about5 Å to about 100 Å, and lithographically-defined conductive via 1582 mayhave a thickness range of about 5 Å to about 100 Å; sensing layerstructure 1624 may have a thickness range of about 10 Å to about 100 Å;capping layer 1620 may have a thickness range of about 5 Å to about 50Å; first and second insulator layers 1660 and 1662 may have a thicknessrange of about 10 Åto about 100 Å; and first and second hard bias layers1664 and 1666 may have a thickness range of about 20 nm to about 200 nm.

As shown, current-constraining structure 1680 of this exemplaryembodiment is formed as part of or within a spacer layer having a firstspacer layer portion (SP-1) and a second spacer layer portion (SP-2).First spacer layer portion SP-1 is formed adjacent sensing layerstructure 1624 (which is located above it), and second spacer layerportion SP-2 is formed adjacent pinned layer structure 1604 (which islocated below it). In this embodiment, current-constraining structure1680 has a single lithographically-defined conductive via 1582surrounded by insulator portions 1642 and 1644 and is located in acenter of the structure. However, any suitable number of preferablyequally-distributed vias may be incorporated within current-constrainingstructure 1680 as will be shown and described later in relation to FIGS.17 and 18.

Width W₁₃ of lithographically-defined conductive via 1582 may be definedrelative to a trackwidth TW_(S16) of CPP read sensor 1600. Preferably,width W₁₃ of lithographically-defined conductive via 1582 is less thanor equal to ½ of a trackwidth TW_(S16) of CPP read sensor 1600. In thisembodiment, the trackwidth TW_(S16) is about 100 nm (with a range of 30to 200 nm) and width W₁₃ is about 10 nm (with a range of 3 to 40 nm).FIG. 16 reveals more clearly that lithographically-defined conductivevia 1582 is formed at a centerline L_(C16) of the width of sensor stackstructure 1602 and trackwidth TW_(S16) of CPP read sensor 1600. For thesingle conductive via, note that a distance D₁₆ defines the width ofeach insulator material portion 1642 and 1644 whereW₁₃+(2*D₁₆)=TW_(S16).

The dimension of lithographically-defined-conductive via 1582 in thestripe height (SH) direction is now discussed in relation to FIGS. 19,20, and 21. In FIG. 19, an isometric illustration of sensor stackstructure 1602 is shown. As illustrated, sensor stack structure 1602 hasa stripe height SH_(S19) associated with it and lithographically-definedconductive via 1582 has a dimension L_(V19) in the stripe heightdirection. In this embodiment, L_(V19)=SH_(S19). More generally,dimension L_(V19) is equal to or less than the stripe height SH_(S19). Atop down illustration taken along line 20-20 of FIGS. 16 and 19 is shownin FIG. 20, which reveals that lithographically-defined conductive via1582 is formed at a centerline L_(C19) of stripe height SH_(S19) ofsensor stack structure 1602. In FIG. 21, a top down illustration of avariation of this exemplary embodiment is shown. Again, alithographically-defined conductive via 2182 has a dimension L_(V21) inthe stripe height direction. In the embodiment of FIG. 21, dimensionL_(V21) of lithographically-defined conductive via 2182 is less than thestripe height SH_(S20). In this case, a distance D₂₁ defines the heightof each insulator material portion where L_(V21)+(2*D₂₁)=SH_(S19). Forthe single conductive via embodiment, lithographically-definedconductive via 2182 is formed at a centerline L_(C19) of stripe heightSH_(S19) of sensor stack structure 1602.

Referring now to FIG. 17, an alternate embodiment of a CPP read sensor1700 of the present disclosure is shown. FIG. 17 is the same as thatshown and described in relation to FIG. 16 except for differences in acurrent-constraining structure 1780 of CPP read sensor 1700. Inparticular, current-constraining structure 1780 is formed with twolithographically-defined conductive vias 1782 and 1784 which are equallyspaced apart from a centerline LC17 of a width of sensor stack structure1702 and a trackwidth S17 of CPP read sensor 1700. Similar to FIG. 16,current-constraining structure 1780 is part of a spacer layer structurewhich has a first spacer layer portion (SP-1) and a second spacer layerportion (SP-2), where the second spacer layer portion SP-2 is formedadjacent sensing layer structure 1624 (which is positioned above it) andthe first spacer layer portion SP-1 is formed adjacent pinned layerstructure 1604 (which is positioned below it). Lithographically-definedconductive vias 1784 and 1784 have conductive materials 1734 formedwithin them, parts of which make up the spacer layer.Lithographically-defined conductive via 1782 is surrounded by insulatormaterials 1742 on the left and insulator materials 1744 on the right.Similarly, lithographically-defined conductive via 1784 is surrounded byinsulator materials 1744 on the left and insulator materials 1746 on theright.

In this embodiment, each width W_(A17) of lithographically-definedconductive vias 1782 and 1784 is chosen such that (2*W_(A17)) is lessthan or equal to ½ of a trackwidth TW_(S17) of CPP read sensor 1700.Lithographically-defined conductive vias 1782 and 1784 are formedequally spaced apart from the centerline L_(C17) of trackwidth TW_(S17)of sensor stack structure 1702 by a distance D_(17A) where(2*W_(A17))+(2*D_(17A))+(2*D_(17B))=TW_(S17). Note that distance D_(17B)may be equal to, less than, or greater than distance D_(17A). Asdiscussed in relation to FIGS. 20-22, lithographically-definedconductive vias 1782 and 1784 have stripe height dimensions as wellwhich may vary.

A method for making such a structure of FIG. 17 is the same as thatdescribed earlier in relation to FIG. 10, except current-constrainingstructure 1780 is formed having the two lithographically-definedconductive vias 1782 and 1784. Here, the photoresist structure is formedwith two openings (e.g. in FIGS. 12-13), etching is performed to createtwo apertures (e.g. in FIGS. 13-14), and deposition is performed withinthe two apertures (e.g. in FIGS. 14-15).

Referring ahead to FIG. 18, an alternate embodiment of a CPP read sensor1800 of the present disclosure is shown. FIG. 18 is the same as thatshown in FIG. 16, except for differences in a current-constrainingstructure 1880 of CPP read sensor 1800. In particular,current-constraining structure 1780 is formed with threelithographically-defined conductive vias 1882, 1884, and 1886 which areequally spaced apart from a centerline L_(C18) of a width of sensorstack structure 1702 and a trackwidth TW_(S17) of CPP read sensor 1700Similar to FIGS. 16-17, current-constraining structure 1880 is part of aspacer layer structure which has a first spacer layer portion (SP-1) anda second spacer layer portion (SP-2), where the second spacer layerportion SP-2 is formed adjacent sensing layer structure 1624 (which islocated above it) and the first spacer layer portion SP-1 is formedadjacent pinned layer structure 1604. Lithographically-definedconductive vias 1882, 1884, and 1886 have conductive materials 1834formed within them, parts of which make up the spacer layer structure.Lithographically-defined conductive via 1882 is surrounded by insulatormaterials 1842 on its left and insulator materials 1844 on its right.Similarly, lithographically-defined conductive via 1884 is surrounded byinsulator materials 1844 on its left and insulator materials 1846 on itsright. Also similarly, lithographically-defined conductive via 1886 issurrounded by insulator materials 1846 on its left and insulatormaterials 1848 on its right.

In this embodiment, each width W_(A18) of lithographically-definedconductive vias 1882, 1884 and 1886 is chosen such that (3*W_(A18)) isless than or equal to ½ of a trackwidth TW_(S18) of CPP magnetic head1800. Lithographically-defined conductive via 1884 is formed at thecenterline L_(C18) of trackwidth TW_(S18) of sensor stack structure1802, whereas lithographically-defined conductive vias 1882 and 1886 areformed equally spaced apart from the centerline L_(C18) by a distanceD_(18A) where (3*W_(A18))+(2*D_(18A))+(2*D_(18B))=trackwidth TW_(S18).Note that distance D_(18B) may be equal to, less than, or greater thandistance D_(18A). As discussed in relation to FIGS. 20-22,lithographically-defined conductive vias 1882, 1884 and 1886 have stripeheight dimensions as well which may vary.

A method for making such a structure of FIG. 18 is the same as thatdescribed in relation to FIG. 10, except current-constraining structure1880 is formed having the three lithographically-defined conductive vias1884, 1884, and 1886. Here, the photoresist structure is formed withthree openings (e.g. in FIGS. 12-13), etching is performed to createthree apertures (e.g. in FIGS. 13-14), and deposition is performedwithin the three apertures (e.g. in FIGS. 14-15).

The CPP sensors of the present disclosure may include all layers shownand described in relation to FIGS. 16-19. However, one skilled in theart understands the layers described in relation to FIGS. 16-19 are buta few examples of all possible CPP sensor layer configurations. Forexample, the CPP sensors are shown as top-type CPP sensors; however thesensors may be bottom-type CPP sensors. Alternative configurations mayinclude dual CPP sensors, in-stack biasing structures, AP-pinned layerstructures, and AP-sensing layer structures, to name a few. In FIG. 22,another embodiment is shown of a dual CPP sensor 2200 which includes acurrent-constraining structure of the present disclosure. As shown inFIG. 22, sensor 2200 includes, from bottom to top, a seed layerstructure 2202 (e.g. Ta/NiFeCr); an antiferromagnetic (AFM) pinninglayer 2204 (e.g. IrMn); an antiparallel (AP) pinned layer structure 2206which includes a first ferromagnetic (FM) layer 2208 (e.g. CoFe), asecond FM layer 2210, and an antiparallel coupling (APC) layer 2212(e.g. Ru) between layers 2208 and 2210; a spacer layer 2214 (e.g. Cu); afree (or sensing) layer 2216 (e.g. Co₂MnGe); a spacer layer structure2218 (within which an electrically-conductive via 2250 of thecurrent-constraining structure is formed) which includes a first spacerlayer portion 2220 (e.g. Cu), a second spacer layer portion 2222 (e.g.Cu), and oxidized metal sublayer structures 2224 and 2226 (e.g. TaOxsublayers); an AP pinned layer structure 2228 which includes a first FMlayer 2230 (e.g. CoFe), a second FM layer 2232, and an APC layer 2234(e.g. Ru) between layers 2230 and 2232; an AFM pinning layer 2236 (e.g.IrMn); and a cap layer 2238 (e.g. Ta).

Further structural variations may also be made. As described above, thecurrent-constraining structure may be formed adjacent the sensing layerstructure, or within or adjacent the capping layer structure.Alternatively, the current-constraining structure may be formed adjacentthe pinned layer structure or the AFM pinning layer structure. Alsodescribed above, the lithographically-defined conductive via may beformed within the spacer layer. Alternatively, however, thelithographically-conductive via may be formed on top of or below thespacer layer, or on top of or below the capping layer.

Particular attention in the description was placed on the relativelocation of the lithographically-defined conductive vias. Specifically,the above embodiments describe the location of thelithographically-defined conductive vias at or equally spaced apart fromthe centerline of the trackwidth of the sensor stack structure and/orthe centerline of the stripe height of the sensor stack structure.Alternatively, the lithographically-defined conductive vias of thepresent disclosure may be formed in any suitable location for propercurrent flow, as in adjacent the ABS. Furthermore, as discussedspecifically in relation to FIG. 22, a current-constraining structure ofthe present disclosure may have lithographically-defined conductive viaswith dimensions in the stripe height direction that are less than thatof the stripe height. However, other configurations are possible. Forexample, a two-dimensional matrix (as viewed from top-down) oflithographically-defined conductive vias may be formed within thecurrent constraining structure. In addition, multiplecurrent-constraining structures of the present disclosure may beutilized per the desires of the user.

Oxidized Metal Sublayer Structure Formation of FIGS. 23-27 for Step 1006of FIG. 10. Conventional approaches and issues in the formation ofoxidized metals from deposited metals are first discussed. Suchconventional methods of forming such oxidized metals involve the stepsof depositing a metallic layer (e.g. between about 20 Å and about 40 Å)in-situ and subsequently exposing that metallic layer to oxygen ex-situto ambient atmosphere. The depth of oxygen (O) diffusion into themetallic layer is difficult to precisely control. Furthermore, the formin which the diffused oxygen is found (if at all) throughout such layeris of importance to sensor performance. Consider the use of tantalum(Ta) as the metal where it is subsequently oxidized. The oxygen maydiffuse only to a certain depth into the metallic layer since theex-situ oxidation is from the top. Only an upper portion of the metalliclayer may be sufficiently oxidized from the ex-situ oxidation. In theupper portion of the layer, the diffused oxygen may be strongly bondedto the Ta in the Ta lattice due to the formation of Ta—O valence bonds,as in the stable compound tantalum oxide (Ta₂O₅). In a middle portion ofthe metallic layer, the diffused oxygen may be loosely bonded in a lowerconcentration than that found in the upper portion, probably ininterstitial sites of the Ta lattice. Non-bonded Ta atoms may also bepresent in the middle portion of the metallic layer. In a lower portionof the metallic layer, diffused oxygen may not be found in anyappreciable concentration (i.e. the lower portion may be substantiallypure Ta). As in the middle portion, non-bonded Ta atoms may be presentin the lower portion. This non-bonded Ta may diffuse into underlyingferromagnetic materials (such as a free or sensing layer structure), andtherefore create a magnetic dead layer within the ferromagneticmaterials. As apparent, the atomic percent oxygen in the resultingstructure will not be uniform throughout from top to bottom, especiallyin a relatively thick deposited structure. On the other hand, if theex-situ oxidation is thorough, the thoroughly-diffused oxygen in themetallic layer will be strongly bonded to all of the Ta in the Talattice due to the formation of Ta—O valence bonds, as in the stablecompound Ta₂O₅. This Ta—O valence bonding increases the thickness of thelayer by a factor of about 2½ times (i.e. Ta₂O₅ layer thickness is 2.5times thicker than the Ta layer thickness). However, underlyingferromagnetic materials may become partially oxidized and form amagnetically “dead” layer from the diffusion of non-bonded oxygen intoit. If the layer were to be sufficiently oxidized uniformly from top tobottom without un-bonded Ta or oxygen diffusion into underlyingferromagnetic materials, the sensor properties may be enhanced asmentioned above. Note that uniform oxidation performed subsequent tometallic layer deposition is practical with metallic layer thicknessesof about 10 Å or less, which is below conventional thicknessrequirements for a spacer layer between about 20 Å and about 100 Å.

The formation of an insulator made of the oxidized metal sublayerstructure of the present disclosure is now described in more detail inrelation to FIGS. 23-27. This process may be used in step 1004 of FIG.10 to create insulator 1140 of FIG. 11. In FIG. 23, a sensor stackstructure having an electrically conductive spacer layer 2302 (e.g. Cu)is formed. Next, an insulator made of an oxidized metal sublayerstructure (such as that described in relation to FIG. 11) is formed overspacer layer 2302. Using a deposition process, metallic materials (e.g.Ta) are deposited over and in contact with spacer layer 2302. The resultis a metallic sublayer 2402 shown in FIG. 24. Preferably, the depositionprocess is a physical vapor deposition process (PVDP) performed in adeposition chamber module. In this exemplary embodiment, the depositionprocess of metallic sublayer 2402 is accomplished in an atmosphere ofargon (Ar) with a sputtering flow of 20 standard cubic centimeters(sccm). The deposition process may alternatively be any suitable thinfilm deposition process, such as ion beam sputtering, evaporation oranother similar method. Furthermore, any other suitable metal orcombinations of metals may be substituted for Ta in metallic sublayer2402 and well as any suitable thickness.

After metallic sublayer 2402 is deposited, the gas is evacuated from thedeposition chamber module. The work-in-progress is then moved,maintaining a vacuum, to an in-situ oxidization module. In the in-situoxidization module, an oxidation process is performed on metallicsublayer 2402. As a result, in FIG. 25 an oxidized metallic sublayer2502 is shown to be formed. The oxidation process is preferably anin-situ plasma oxidation process, which is suitably controlled and timedsuch that a sufficiently oxidized tantalum oxide layer with uniformatomic percent oxygen throughout the layer from top to bottom isachieved. The reactant gas used in the oxidation process includes, forexample, an oxygen having a flow of 4 sccm and argon having a flow of 20sccm. The oxidation process for a 6⅔ Å Ta layer (which produces about16⅔ Å of Ta₂O₅) may be performed for about 1 minute at room temperature.The RF power applied to the substrate may be 20 watts (W). However, theflow of oxygen in the reactant gas may vary from about 2 sccm to about10 sccm and the RF power may vary from 10 W to 40 W, for example.Further, the oxidation process may be performed from about ¼ minutes to6 minutes corresponding to a range of metallic sublayer thicknesses fromabout 1 Å to about 10 Å. Note that the oxidation process mayalternatively utilize any suitable oxidation process, such as naturaloxidation, radical shower oxidation, or reactive sputtering oxidation.

Next, it is identified whether the above steps need to be repeated. Thiswill depend on the number of oxidized metallic sublayers desired.Repeating these steps forms a laminated layer structure, and morespecifically the plurality of oxidized metallic sublayers of theinsulator. In this example, the steps are repeated only once to producea total of two (2) sublayers in the structure. In a repeated depositionprocess of FIG. 26, metallic materials are deposited over and adjacentoxidized metallic layer 2502. Preferably, this deposition process is thesame deposition process using the same metallic materials utilized indeposition process of FIG. 2402. The result is shown in FIG. 26 where ametallic sublayer 2602 is formed over oxidized metallic sublayer 2502. Arepeated oxidization process is then performed to transform metallicsublayer 2602 into an oxidized metallic sublayer 2702 shown in FIG. 27.Preferably, this oxidization process is the same oxidization processusing the same components utilized in oxidization process of FIG. 25. Asa result, an insulator is formed with a plurality of two oxidizedmetallic sublayers. In this embodiment, the insulator has a resultingthickness of about 20 Å.

The total thickness of the insulator, the sublayer thickness, the numberof sublayers, the materials of each sublayer, and the processing of eachsublayer may be chosen by design to achieve the specular reflectivestructure and give suitable desired effects on the magnetoresistiveeffect and other soft magnetic properties of the sensor. As thethicknesses of the sublayers may vary per the design, it is desired thatany such process will oxidize each sublayer sufficiently from top tobottom without over-oxidizing. Thus, the variables for sufficientoxidization of each sublayer (e.g. time, flow rate, and power) arepreferably selected and confirmed through empirical analysis prior tolarge-scale manufacturing. In particular, the values of the variables(e.g. time, flow rate, and power) which correspond to desired or optimalsensor performance are those selected for the oxidization forlarge-scale manufacturing. This is later discussed further in relationto the graphs of FIGS. 28-32.

Note that the oxidation process associated with FIG. 25 mayalternatively be a nitridation process or an oxynitridation process. Inthe case of the nitridation process, a metal nitride is formed. Thenitridation process preferably is an in-situ plasma nitridation process,where a sufficiently nitrided metal layer with uniform atomic percentnitrogen is formed. The nitridation of a metallic layer by thenitridation process is suitably controlled and timed such that asufficiently nitrided tantalum nitride layer with uniform atomic percentnitrogen throughout the layer from top to bottom is achieved. Thenitridation process may alternatively be any suitable nitridationprocess such as natural nitridation, radical shower nitridation, orreactive sputtering nitridation. These processes may be performedin-situ with other processing steps. In the case of the oxynitridationprocess, a metal oxynitride is formed. The oxynitridation processpreferably is an in-situ plasma oxynitridation process, where asufficiently oxynitrided metal layer with uniform atomic percent oxygenand uniform atomic percent nitrogen is formed. The oxynitridation of ametallic layer by the oxynitridation process is suitably controlled andtimed such that a sufficiently oxynitrided tantalum oxynitride layerwith uniform atomic percent oxygen and uniform atomic percent nitrogenthroughout the layer from top to bottom is achieved. The oxynitridationprocess may alternatively be any suitable oxynitridation process, suchas natural oxynitridation, radical shower oxynitridation, or reactivesputtering oxynitridation. These processes may be performed in-situ withother processing steps. A DC magnetron system suitable for use in themethod corresponding to FIGS. 23-27 may be sold by Anelva TechnixCorporation of Japan. Alternatively, an magnetron/ion beam sputteringsystem may be purchased from Veeco Corporation of Plainview, N.Y.

Again, with use of the process of oxidation, nitridation, oroxynitridation on each metal sublayer, degradation of the spacer layeris reduced or eliminated such that the desirable soft magnetics of thefree layer in the read sensor are maintained.

Note that the insulator comprising the oxidized metal sublayer structureis a specular reflective insulator structure. The sublayers are oxidizedseparate and apart from each other, therefore resulting in precisecontrol over respective sublayer and structure characteristics.Advantageously, each oxidized metallic sublayer is sufficientlyuniformly oxidized so as to increase the giant magnetoresistive effectand improve soft magnetic properties of the read sensor. This sensor ispreferably embodied in a magnetic head and disk drive as describedearlier in relation to FIGS. 1-9.

In general, the oxidized metal sublayer structure of the presentdisclosure has n sublayers, preferably each with an equal thickness h₁₂,such that n*h₁₂ is equal to a total thickness H₁₂ of Ta₂O₅. Totalthickness H₁₂, sublayer thickness h₁₂, and the number of sublayers n maybe chosen by design to give suitable desired effects on themagnetoresistive effect and other soft magnetic properties of thesensor. In one example, the oxidized metal sublayer structure has threesublayers. In this case, the oxidized metal sublayer structure has atotal thickness H₁₂ corresponding to about 15 Å where each sublayer hasan equal thickness h₁₂ corresponding to about 15 Å (3*5 Å=15 Å). Thus,the oxidized metal sublayer structure may have any suitable number ofsublayers such as two, four, or more sublayers. Total thickness H₁₂ maybe within a wide range of values (e.g. about 10 Å to about 100 Å), andthickness h₁₂ may also be within a wide range of values (e.g. about 2.5Å to about 25 Å). As a further example, the oxidized metal sublayerstructure may have four (4) sublayers where each sublayer has athickness of about 5 Å for a total thickness of about 20 Å. As anotherexample, the oxidized metal sublayer structure may have two (2)sublayers where each sublayer has a thickness of about 10 Å for a totalthickness of about 20 Å. As yet another example, the oxidized metalsublayer structure may have four (4) sublayers where each sublayer has athickness of about 16⅔ Å for a total thickness of about 66⅔ Å. Asdiscussed, preferably the thickness of each sublayer is the same;however, the thickness of each sublayer may alternatively be different.

In the exemplary embodiment, the oxidized metal sublayer structure is auniform structure of oxidized metal of tantalum, namely Ta₂O₅. Eachsublayer is sufficiently independently oxidized from top to bottom intoTa₂O₅ so that the entire oxidized metal sublayer structure is a uniformstructure of Ta₂O₅ from top to bottom. The diffused oxygen is stronglybonded to the Ta in the Ta lattice due to the formation of Ta—O valencebonds. Since each sublayer has uniform atomic percent oxygen from top tobottom, the entire oxidized metal sublayer structure has uniform atomicpercent oxygen from top to bottom. Preferably, all of the sublayers ofthe oxidized metal sublayer structure are formed in direct contact witheach other with no intervening layers or materials between them. Withappropriate characterization techniques, the distinct interfaces betweensublayers of the oxidized metal sublayer structure may be observed.Alternatively, intervening layers may exist between the sublayers.

Although Ta was discussed in relation to the structure, any suitablematerial may be used where the structure may still perform itsappropriate function. Instead of Ta, for example, the metal used in thestructure may be or include hafnium (Hf), zirconium (Zr), titanium (Ti),aluminum (Al), magnesium (Mg), yttrium (Y), chromium (Cr), niobium (Nb),molybdenum (Mo), tungsten (W), vanadium (V), rhenium (Re), scandium(Sc), or silicon (Si). As discussed, preferably the material of eachsublayer is the same; however, the material of each sublayer mayalternatively be different. Furthermore, combinations like alloys of twoor more metals may be used. In binary and multi-component systems, suchas the Ta and oxygen system, intermediate phases (stable or metastable)may occur. Thermodynamically, the composition of any such phase isvariable and they are called stoichiometric phases. Ta₂O₅ is thepreferred stoichiometric phase in the present disclosure due to its highstability and specular reflectivity. However, other stoichiometricphases in the Ta and oxygen system, such as tantalum monoxide (TaO) andtantalum dioxide (TaO₂) may be present as alternatives.

Instead of an oxide of metal (e.g. Ta₂O₅), a nitride of metal (e.g.,TaN, Ta₂N, Ta₃N₅, etc.) may be utilized in the structure. In thisembodiment, each sublayer is sufficiently independently nitrided fromtop to bottom into Ta₂N, so that the entire structure is uniform Ta₂Nfrom top to bottom. The diffused nitrogen is strongly bonded to the Tain the Ta lattice due to the formation of Ta—N valence bonds. Since eachsublayer has uniform atomic percent nitrogen from top to bottom, theentire structure has uniform atomic percent nitrogen from top to bottom.Also alternatively, an oxynitride of metal (e.g. TaON, etc.) mayalternatively be used in the structure. In this embodiment, eachsublayer is sufficiently independently oxidized/nitrided from top tobottom into TaON, so that the entire structure is uniform TaON from topto bottom. The diffused oxygen and nitrogen are strongly bonded to theTa in the Ta lattice due to the formation of Ta—O—N valence bonds. Sinceeach sublayer has a uniform atomic percent oxygen and uniform atomicpercent nitrogen from top to bottom, the entire structure has uniformatomic percent oxygen and atomic percent nitrogen from top to bottom.Further, the sublayers of structures of the present disclosure may varyin composition being combinations of oxides, nitrides, and oxynitrides.

Illustrative Graphical Data of FIGS. 28-32 Pertaining to the OxidizedMetal Sublayer Structure. FIGS. 28-32 are various graphs showingillustrative data for the insulator (e.g. the oxidized metal sublayerstructure) utilized in the current-constraining structures. Inparticular, FIG. 28 is a graph showing illustrative data for low field(LF) giant magnetoresistance (GMR) versus oxygen flow rate when one,two, and four sublayers of Ta (0.5 nm thickness) are utilized. In FIG.29, a graph showing illustrative data for coercivity Hc (easy and hard)versus oxygen flow rate for the same structure is shown. In general,FIGS. 28-29 reveal that good magnetics may be achieved and optimized inthe selection of a suitable oxygen flow rate. FIG. 30 is a graph showingillustrative data for LF GMR versus Ta sublayer thickness. FIG. 31 is agraph showing illustrative data for coercivity H_(ce) (easy) versus Tasublayer thickness, and FIG. 32 is a graph showing illustrative data forcoercivity H_(ch) (hard) versus Ta sublayer thickness. In the data takenfor graphs in FIGS. 30-32, the number of repeats were varied (N=2, 3, 4,and 5) so that (Ta×N) was about 20 Å. All data were taken using 1.5 sccm(standard centimeter cube per minute) O₂ flow, except at the Ta=20 Åmark (N=1) which was not oxidized. For 3.3-4 Å Ta sublayer thickness,1.5 sccm O₂ flow was close to optimal, and showed LF GMR=16.2%,H_(ce)=4.4.5 Oe, and H_(ch)=1-2 Oe.

Thus; current-perpendicular-to-plane (CPP) read sensors havingconstrained current paths made of lithographically-defined conductivevias with surrounding oxidized metal sublayers, and methods of makingthe same, have been described. In one illustrative example, at leastpart of a sensor stack structure which includes an electricallyconductive spacer layer is formed. A metal sublayer is deposited overand adjacent the spacer layer, followed by one of an oxidation process,a nitridation process, and an oxynitridation process, to produce aninsulator (e.g. an oxidized metal) from the metal sublayer. The metalsublayer deposition and oxidation/nitridation/oxynitridation processesare repeated as necessary to form the insulator with a suitablethickness. Next, a resist structure which exposes one or more portionsof the insulator is formed over the insulator. With the resist structurein place, exposed insulator materials are removed by etching to form oneor more apertures through the insulator down to the spacer layer.Electrically conductive materials are subsequently deposited within theone or more apertures to form one or more lithographically-definedconductive vias of a current-constraining structure. Advantageously, thelithographically-defined conductive vias increase the current density ofthe read sensor in the region of the sensing layers to therebysimultaneously increase its resistance and magnetoresistance. With useof the process of oxidation, nitridation, or oxynitridation on eachmetal sublayer, degradation of the spacer layer is reduced or eliminatedsuch that the desirable soft magnetics of the free layer in the readsensor are maintained. The size and number of vias may be varied andselected so as to precisely “tune” the sensor's resistance andmagnetoresistance. As there is increasing evidence that themagnetoresistive effect is reduced near edges of the read sensor frommilling damage, it is also advantageous to isolate a single or few viasin the center of the sensor structure to avoid such damage.

It is to be understood that the above is merely a description ofpreferred embodiments of the invention and that various changes,alterations, and variations may be made without departing from the truespirit and scope of the invention as set for in the appended claims. Fewif any of the terms or phrases in the specification and claims have beengiven any special meaning different from their plain language meaning,and therefore the specification is not to be used to define terms in anunduly narrow sense.

1. A method of making a current-perpendicular-to-plane (CPP) read sensorhaving a constrained current path, comprising: forming at least part ofa sensor stack structure of the read sensor; depositing a metal sublayerover and adjacent an electrically conductive layer of the sensor stackstructure, the electrically conductive layer forming at least part of aspacer layer of the sensor stack structure; performing, on the metalsublayer, one of an oxidation process, a nitridation process, and anoxynitridation process, to produce an insulator from the metal sublayer;repeating the steps of depositing and performing; forming a resiststructure over the insulator which exposes materials of the insulator;etching, with the resist structure in place, to remove the exposedmaterials of the insulator to thereby form one or more apertures throughthe insulator down to the electrically conductive layer; and formingelectrically conductive materials within the one or more apertures toform one or more lithographically-defined conductive vias of acurrent-constraining structure of the read sensor.
 2. The method ofclaim 1, wherein the step of performing comprises performing theoxidation process on the metal sublayer, and wherein the insulatorcomprises a plurality of oxidized metal sublayers.
 3. The method ofclaim 1, wherein the metal sublayer comprises tantalum (Ta).
 4. Themethod of claim 1, wherein the step of depositing the metal sublayercomprises depositing a metal sublayer comprising tantalum (Ta), andwherein the step of performing comprises performing the oxidizationprocess to thereby produce an insulator comprising a plurality ofoxidized tantalum (TaOx) sublayers.
 5. The method of claim 1, whereinthe one or more apertures comprise a single aperture through a center ofthe read sensor.
 6. The method of claim 1, further comprising: repeatingthe steps of depositing and performing at least two times.
 7. The methodof claim 1, further comprising: repeating the step of depositing andperforming at least three times.
 8. A current-perpendicular-to-plane(CPP) read sensor having a constrained current path, the CPP read sensorcomprising: a sensor stack structure; a current-constraining structureof the sensor stack structure formed adjacent an electrically conductivelayer of the sensor stack structure; the current-constraining structurecomprising a lithographically-defined conductive via surrounded by aninsulator; and the insulator of the current-constraining structurecomprising a plurality of oxidized metal sublayers.
 9. The read sensorof claim 8, wherein each oxidized metal sublayer comprises a tantalumoxide (TaOx) sublayer.
 10. The read sensor of claim 8, furthercomprising: the electrically conductive layer comprising at least partof a spacer layer of the read sensor.
 11. The read sensor of claim 8,further comprising: a free layer; and the electrically conductive layercomprising at least part of a spacer layer which is adjacent the freelayer.
 12. The read sensor of claim 8, further comprising: thelithographically-defined conductive via comprising a single conductivevia in a center of the read sensor.
 13. The read sensor of claim 8,wherein the plurality of oxidized metal sublayers comprise at least fouroxidized metal sublayers.
 14. The read sensor of claim 8, wherein eachoxidized metal sublayer alternatively comprises one of a nitrided metalsublayer and an oxynitrided metal sublayer.
 15. A disk drive comprising:a housing; a magnetic disk rotatably supported in the housing; amagnetic head; a support mounted in the housing for supporting themagnetic head so as to be in a transducing relationship with themagnetic disk; a spindle motor for rotating the magnetic disk; anactuator positioning means connected to the support for moving themagnetic head to multiple positions with respect to said magnetic disk;a processor connected to the magnetic head assembly, to the spindlemotor, and to the actuator for exchanging signals with the magnetic headfor controlling movement of the magnetic disk and for controlling theposition of the magnetic head; the magnetic head assembly including aread head having a CPP read sensor; the CPP read sensor including: asensor stack structure; a current-constraining structure of the sensorstack structure formed adjacent an electrically conductive layer of thesensor stack structure; the current-constraining structure comprising alithographically-defined conductive via surrounded by insulator layers;and each insulator layer of the current-constraining structurecomprising a plurality of oxidized metal sublayers.
 16. The disk driveof claim 15, wherein each oxidized metal sublayer of the CPP read sensorcomprises a tantalum oxide (TaOx) sublayer.
 17. The disk drive of claim15, further comprising: the electrically conductive layer of the CPPread sensor comprising at least part of a spacer layer of the readsensor.
 18. The disk drive of claim 15, wherein the CPP read sensorfurther comprises: a free layer; and the electrically conductive layercomprising at least part of a spacer layer which is adjacent the freelayer.
 19. The disk drive of claim 15, further comprising: thelithographically-defined conductive via of the CPP read sensorcomprising a single conductive via in a center of the read sensor. 20.The disk drive of claim 15, wherein the plurality of oxidized metalsublayers comprise at least four sublayers.